Dies used in extrusion processes have long been used to produce a sheet or web of a formable material, such as a thermoplastic. In such a die, some provision is typically made to permit adjustment of the width of the formed product. In the past, this has been accomplished through the use of deckles mounted either within the die manifold or cavity or outside the die adjacent the die outlet. The deckles restrict material flow to a space therebetween and the positions thereof are adjustable to permit the width of the formed product to be controlled. Often, the deckles are shaped to minimize or eliminate a condition known as edge bead wherein the edges of the formed product are thicker than the remaining portions of the product.
Maejima, U.S. Pat. No. 4,659,302 discloses a T-shaped extrusion die including a pair of deckle structures disposed within the manifold on each side of the die for regulating the width of the extruded film. Each deckle structure includes a pair of inner deckles and an inner deckle rod. Each deckle rod includes a tip with a tongue-shaped protrusion for regulating the width of the film without forming edge beads at both edges thereof.
Maejima, U.S. Pat. No. 4,248,579 discloses a film extrusion die like that disclosed in the '302 patent described above, except that each pair of inner deckles is replaced by a single deckle and each deckle rod having a protrusion is replaced by a straight deckle rod without a protrusion.
When using deckles to regulate the width of an extruded product, it is usually necessary to stop extrusion of product through the die, open the die lip gap to permit movement of the deckles, adjust the deckle positions, readjust the die lip gap to the desired dimension, restart extrusion, observe the effect on the extruded product and readjust the deckle positions of the extruded product if unsatisfactory. Further, in the case of multi-component deckle systems like that disclosed in the '302 patent described above, the profiles of the internal deckles must often be adjusted by machining or other means in order to manufacture a suitable product. This adjustment of the deckle profile must be undertaken off-line before production, potentially resulting in the need to repetitively disassemble the die, adjust the deckle profiles and positions, reassemble the die and test the die operation before a suitable deckle profile and/or positions are found. To date, no satisfactory method has been found by which the deckle positioning and profile adjustment steps can be undertaken in a rapid and efficient manner either off-line or during manufacture of the extruded product.
In addition to the foregoing, extrusion dies are often used to extrude materials which are corrosive, particularly at high extrusion temperatures. The corrosive nature of some materials result in pitting and deterioration of the die surfaces, particularly the portion of the die forming the die outlet, resulting in the need to repair and/or remanufacture the die. Still further, it is sometimes necessary to modify the die outlet to achieve proper flow of a particular product. In the past, such repair or modification results in significant down time and considerable expense.
In addition, it is necessary to provide some type of sealing apparatus at the point where the rods supporting the internal deckles exit the die body. Such sealing is difficult to achieve, particularly given the corrosive nature of the extruded material and the high temperatures at which the die body is maintained.